A family of GTP binding proteins and related proteins has been implicated in tumorgenicity of hyperproliferative cells. These proteins include dbl, ect2, lbc, ost, and TIM. See, respectively, Ron et al., EMBO J 7: 2465-2473 (1988); Miki et al., Nature 362: 462-465 (1993); Toksoz et al., Oncogene 9(2): 641-628 (1994); Horii et al., EMBO J 13(20): 4776-4786 (1994); Chan et al., Oncogene 9(4): 1057-1063 (1994). Also, included in this family is the Tiam-1 protein. This protein has been shown to modulate the invasive potential of a cell. See Habets et al., Cell 77: 537-549 (1994); Habets et al., Oncogene 10(7): 1371-1376 (1995); and Gasion etal., Nature 375: 338-340 (1995). Tiam-1 also has been identified as a member of a family of GDP dissociation stimulators (GDSs). These proteins activate Rho-like and Rac-like GTPases.